From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
To: "Medvedkin, Vladimir" <vladimir.medvedkin@intel.com>,
"Ruifeng Wang (Arm Technology China)" <Ruifeng.Wang@arm.com>,
"bruce.richardson@intel.com" <bruce.richardson@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>,
Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
nd <nd@arm.com>, nd <nd@arm.com>
Subject: Re: [dpdk-dev] [PATCH v3 3/3] lib/lpm: memory orderings to avoid race conditions for v20
Date: Sat, 29 Jun 2019 17:35:23 +0000 [thread overview]
Message-ID: <VE1PR08MB51494C8B025F78478CB3DAEA98FF0@VE1PR08MB5149.eurprd08.prod.outlook.com> (raw)
In-Reply-To: <6daf7a76-1def-21df-d202-10b2a8f8582a@intel.com>
<snip>
>
> As a general remark consider writing all of the tbl entries including
> tbl8 with atomic_store. Now "lpm->tbl8[j] = new_tbl8_entry;" is looks like
>
> 1e9: 44 88 9c 47 40 01 00 mov
> %r11b,0x2000140(%rdi,%rax,2) <-write first byte
> 1f0: 02
> 1f1: 48 83 c0 01 add $0x1,%rax
> 1f5: 42 88 8c 47 41 01 00 mov %cl,0x2000141(%rdi,%r8,2) <-write
> second byte
> 1fc: 02
>
> This may cause an incorrect nexthop to be returned. If the byte with valid flag
> is updated first, the old(and maybe invalid) next hop could be returned.
+1
It is surprising that the compiler is not generating a single 32b store. As you mentioned 'relaxed' __atomic_store_n should be good.
>
> Please evaluate performance drop after.
>
> --
> Regards,
> Vladimir
next prev parent reply other threads:[~2019-06-29 17:35 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-27 9:37 [dpdk-dev] [PATCH v3 1/3] lib/lpm: not inline unnecessary functions Ruifeng Wang
2019-06-27 9:37 ` [dpdk-dev] [PATCH v3 2/3] lib/lpm: memory orderings to avoid race conditions for v1604 Ruifeng Wang
2019-06-27 9:37 ` [dpdk-dev] [PATCH v3 3/3] lib/lpm: memory orderings to avoid race conditions for v20 Ruifeng Wang
2019-06-28 13:33 ` Medvedkin, Vladimir
2019-06-29 17:35 ` Honnappa Nagarahalli [this message]
2019-07-05 13:45 ` Alex Kiselev
2019-07-05 16:56 ` Medvedkin, Vladimir
2019-07-01 7:08 ` Ruifeng Wang (Arm Technology China)
2019-06-27 15:24 ` [dpdk-dev] [PATCH v3 1/3] lib/lpm: not inline unnecessary functions Stephen Hemminger
2019-06-28 2:44 ` Ruifeng Wang (Arm Technology China)
2019-06-28 4:34 ` Stephen Hemminger
2019-06-28 5:48 ` Ruifeng Wang (Arm Technology China)
2019-06-28 13:47 ` Medvedkin, Vladimir
2019-06-28 13:57 ` Honnappa Nagarahalli
2019-06-28 14:16 ` Medvedkin, Vladimir
2019-06-28 15:35 ` Stephen Hemminger
2019-07-01 6:44 ` Ruifeng Wang (Arm Technology China)
2019-07-05 10:40 ` Medvedkin, Vladimir
2019-07-05 10:58 ` Ruifeng Wang (Arm Technology China)
2019-07-05 10:31 ` Medvedkin, Vladimir
2019-07-05 13:37 ` Alex Kiselev
2019-07-05 16:53 ` Medvedkin, Vladimir
2019-06-28 13:38 ` Medvedkin, Vladimir
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